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percolate:synced-cron

A simple cron system for Meteor. It supports syncronizing jobs between multiple processes. In other words, if you add a job that runs every hour and your deployment consists of multiple app servers, only one of the app servers will execute the job each time (whichever tries first).

Migrated from percolate:synced-cron littledata:synced-cron

Since the original creator of the project could no longer maintain it, we had to migrate the package to another organisation to allow further maintenance and updates.

To migrate you can simply run

$ meteor remove percolate:synced-cron && meteor add littledata:synced-cron

Installation

$ meteor add littledata:synced-cron

API

Basics

To write a cron job, give it a unique name, a schedule and a function to run like below. SyncedCron uses the fantastic later.js library behind the scenes. A Later.js parse object is passed into the schedule call that gives you a huge amount of flexibility for scheduling your jobs, see the documentation.

SyncedCron.add({
  name: 'Crunch some important numbers for the marketing department',
  schedule: function(parser) {
    // parser is a later.parse object
    return parser.text('every 2 hours');
  },
  job: function() {
    var numbersCrunched = CrushSomeNumbers();
    return numbersCrunched;
  }
});

To start processing your jobs, somewhere in your project add:

SyncedCron.start();

Advanced

SyncedCron uses a collection called cronHistory to syncronize between processes. This also serves as a useful log of when jobs ran along with their output or error. A sample item looks like:

{ _id: 'wdYLPBZp5zzbwdfYj',
  intendedAt: Sun Apr 13 2014 17:34:00 GMT-0700 (MST),
  finishedAt: Sun Apr 13 2014 17:34:01 GMT-0700 (MST),
  name: 'Crunch some important numbers for the marketing department',
  startedAt: Sun Apr 13 2014 17:34:00 GMT-0700 (MST),
  result: '1982 numbers crunched'
}

Call SyncedCron.nextScheduledAtDate(jobName) to find the date that the job referenced by jobName will run next.

Call SyncedCron.remove(jobName) to remove and stop running the job referenced by jobName.

Call SyncedCron.stop() to remove and stop all jobs.

Call SyncedCron.pause() to stop all jobs without removing them. The existing jobs can be rescheduled (i.e. restarted) with SyncedCron.start().

To schedule a once off (i.e not recurring) event, create a job with a schedule like this parser.recur().on(date).fullDate();

Configuration

You can configure SyncedCron with the config method. Defaults are:

  SyncedCron.config({
    // Log job run details to console
    log: true,

    // Use a custom logger function (defaults to Meteor's logging package)
    logger: null,

    // Name of collection to use for synchronisation and logging
    collectionName: 'cronHistory',

    // Default to using localTime
    utc: false,

    /*
      TTL in seconds for history records in collection to expire
      NOTE: Unset to remove expiry but ensure you remove the index from
      mongo by hand

      ALSO: SyncedCron can't use the `_ensureIndex` command to modify
      the TTL index. The best way to modify the default value of
      `collectionTTL` is to remove the index by hand (in the mongo shell
      run `db.cronHistory.dropIndex({startedAt: 1})`) and re-run your
      project. SyncedCron will recreate the index with the updated TTL.
    */
    collectionTTL: 172800
  });

Logging

SyncedCron uses Meteor's logging package by default. If you want to use your own logger (for sending to other consumers or similar) you can do so by configuring the logger option.

SyncedCron expects a function as logger, and will pass arguments to it for you to take action on.

var MyLogger = function(opts) {
  console.log('Level', opts.level);
  console.log('Message', opts.message);
  console.log('Tag', opts.tag);
}

SyncedCron.config({
  logger: MyLogger
});

SyncedCron.add({ name: 'Test Job', ... });
SyncedCron.start();

The opts object passed to MyLogger above includes level, message, and tag.

• level will be one of info, warn, error, debug.
• message is something like Scheduled "Test Job" next run @Fri Mar 13 2015 10:15:00 GMT+0100 (CET).
• tag will always be "SyncedCron" (handy for filtering).

Caveats

Beware, SyncedCron probably won't work as expected on certain shared hosting providers that shutdown app instances when they aren't receiving requests (like Heroku's free dyno tier or Meteor free galaxy).

Contributing

Write some code. Write some tests. To run the tests, do:

$ meteor test-packages ./

License

MIT. (c) Percolate Studio, originally designed and built by Zoltan Olah (@zol), now community maintained.

Synced Cron was developed as part of the Verso project.